1. Field of the Invention
The present invention relates to a barrier opening and closing mechanism for a camera, for coupling with the extension and retraction of a lens barrel so as to open and close a lens barrier.
2. Description of the Related Art
Cameras where a lens barrel is extended from a camera body and photographs are then taken are typically provided with a lens barrier opening and closing mechanism for opening a lens barrier at the front end of the lens barrel when extending the lens barrel from a completely retracted position (a position where the lens barrel is housed within the camera body) towards a wide-angle end (position where wide-angle photography is possible) and closing the lens barrier (lens cover) when retracting the lens barrel from the wide-angle position to the completely retracted position.
For example, a barrier opening and closing mechanism (first related technology) disclosed in Japanese Patent No. 2612128 comprises urging means (a spring) for urging a lens barrier in an opening direction, closing means moving in accompaniment with a lens system so as to close the lens barrier, and means for disconnecting the barrier closing means so as to open the lens barrier using the urging force of the urging means when the lens system is in an extended position and establishing a link with the lens barrier closing means in accompaniment with movement of the lens system from the extended position towards the retracted position so as to resist the urging force of the urging means and close the lens barrier.
With, for example, a barrier opening and closing mechanism (second related art) disclosed in Japanese Utility Model Publication No. 7(1995)-55545, a key that advances in a rectilinear manner along the optical axis in accompaniment with extension or retraction of a lens barrel is provided at a lens barrel capable of extending from or retracting towards a camera body. A cam section constituted by an inclined plane is then provided at the front end of this key. A coupling ring arranged so as to come into contact with this inclined surface and rotating as a result of the motion of the key so as to open and close the lens barrier is also provided. FIGS. 24A and 24B are views describing the related art.
With this barrier opening and closing mechanism, when the lens barrel is retracted towards the camera body-side, the coupling ring comes into contact with the cam section and rotates in accordance with the incline so that the lens barrier is closed. On the other hand, as shown in FIG. 24A, when the lens barrel is extended, the key A moves along the optical axis in a direction away from the coupling ring B so that the coupling ring B rotates in accordance with the incline of the cam section C' due to this movement, with the lens barrier opening as a result.
However, in the first related technology, when the lens system is in the extended position, the coupling of the lens barrier and barrier closing means is broken, and the lens barrier is held open only by the urging force of the urging means. The barrier opening operation therefore becomes unreliable when the urging force of the spring becomes weaker due to variations caused by aging etc.
In the second related technology, when the moving distance from the completely retracted position to the wide-angle end is short for the lens barrel, the rotating force of the coupling member B is insufficient and the lens barrier cannot be opened and closed in a smooth manner. In this case, because the extent to which the key A moves is small, it is necessary to make the angle of inclination of the cam section C' shallow, as shown in FIG. 24B so that when the coupling member B is rotated to bring the lens barrier to the closed position, a slight movement of the key A causes the coupling ring B to rotate a substantial amount. However, when the cam section C' is configured in this way, transmission of force from the cam section C' to the coupling ring B is not efficient, and when the friction between the portions of the cam section C' and the coupling ring B that make contact with each other is substantial, the coupling ring does not rotate smoothly.
In order to resolve the aforementioned situation, it is a first problem of the present invention to provide a barrier opening and closing mechanism with a smooth and reliable lens barrier opening and closing operation.
In the aforementioned related technology, it is necessary to provide a cam section constituted by an inclined surface at a key member that moves in a rectilinear manner along the optical axis together with the extending and retracting of the lens barrel, and this cam section has been difficult to make.
In order to resolve the aforementioned situation, it is a second problem of the present invention to provide a barrier opening and closing mechanism with a smooth and reliable lens barrier opening and closing operation and which is also easy to make.